I think one of the things lacking in the gangs, is the character of the individuals. Meeting the individual gangers. Short of going up to the gang, and attempting to get each individual talking to you in some manner, really it's going to be a long time before it would feel like you have any reasonable relationship with a gang.
I mean, I'm sure all the gangers have their backstories, motivations, their own character. But how do you as an outsider interact with that? What makes JoeBaka2013 different from JoeBaka3102, aside one likes to wear their pants low? And 2013 was a cunt that time when he mugged you, while 3102 was business like?
I think there needs to be some process whereas an outsider, you get a chance to learn the difference between the Sinners, and the Snakes, and the Arteries. Outside of just. "Choose a gang you like the theme of, and run with it." As I don't imagine a new player is going to know very much the difference in the gangs.
Maybe have a 'campfire' nights. Gangs gather around their trash-cans, stoking the pieces of burning furniture and garbage that they pulled off the street. Gangers coming forward to tell stories, about how they became legends. You could script this up much the way one scripts a TV show.
It doesn't even have to be a formal thing, just script a ganger here or there to spontaneous ramble off something about themselves, or the gang to a group of urchins, or bragging to a fellow snake or something.
I can type up an example of what I mean if you like.
But yeah, have the gangers chatting, or A ganger showing off to prospects as he makes them clean the street out front of one of the local businesses. Adding ambience and explaining some of the gang, and gangers character(s).
Which is something you can tie in later if you want a gang initiation.
Put in true and false rumours about what the initiation is. Have people say they had to fight park dogs. Bring a dead judge. Slap their mothers, whatever.
This doesn't solely have to be scripted events, or solely NPCs. Organize the players for a day a month to go out and brag to those that pass by, tell stories. Puppet an NPC, a lieutenant or gang leader. "This is why the other group's a bitch. Because this one time we did this."
Sorry if I ranted a bit, or if the ideas are rubbish, he.